Design considerations for development of cuffed endotracheal tube for small airways
Pediatric Anesthesia
Submitted May 2025 by Dr Cedric Sottas
Read by 14 Journal Watch subscribers
Introduction
This paper and the work relating to the design of endotracheal tubes specifically for the paediatric population was sponsored and funded by Medtronic.
The article begins by introducing technical aspects of designing paediatric endotracheal tubes, and is similar to a bench to bedside study, with no mention of specific endotracheal tubes currently on the market.
The aspects of design considered include:
- Endotracheal tube length
- Cuff position
- Murphy eye
- Depth of insertion
- Cuff Shape
- Resting cuff diameter
- Material
While most aspects of this article are well known to clinicians experienced in paediatric airways, it can be seen as a refresher that expands on lesser-known aspects like the choices of materials used.
Summary
To further break down these design considerations:
Endotracheal tube length
Authors cite previously published studies for calculating the distance between carina and cricoid cartilage. The measurements and references are summarized in table 1.
Cuff position
As the cuff should be between cricoid and carina, authors describe calculations based on partial data to estimate the length of the trachea as well as the distance from the vocal cords to the cricoid and infer the length available for a cuff
Murphy eye
The authors state their decision not to include a Murphy eye, which is in accordance with other paediatric cuffed ETTs.
Depth of insertion
The paper describes this calculation with the tip of the tube being at 2/3 of the total distance between the carina and the cricoid, which in turns allows determination of the distance where markings should be made on the tube to help guide the clinician. The risks of putting the marks too proximal or too distal are also described.
Cuff shape
This topic is most relevant to the paediatric population. The authors describe the different types of cuff: - Tight to shaft; which does not allow reliable measurement of the pressure transmitted to the trachea wall - High volume low pressure; which allow those measurements, but could have the disadvantage of a larger than trachea diameter, with folds or creases appearing in the cuff, potentially causing microaspirations - Low volume, low pressure; These are further subdivided into cylindrical and tapered shape, the latter being described as potentially less injury provoking on the tracheal wall (animal study)
Resting cuff diameter
The authors state that the ideal resting cuff diameter for an ETT is approximately 120% of the largest cross-sectional area of an age-related trachea from previous published data - bearing in mind the heterogeneity of resting cuff diameter. There is some detail on the risk of having an undersized and oversized cuff but no solution to this problem.
Material
The paper describes that the material used in making the ETT could be absorbed and lead to toxicity (such as with DEHP). The materials used are mainly PVC and PU. The authors argue that PU is superior, with potentially less microaspirations. They acknowledge the fact this is not a clinically proven fact, with differing results between studies, and it should be noted that costs are higher with PU.
